For many years, ultrasonic surgical instruments have been used for soft tissue cutting and coagulation. These ultrasonic instruments include ultrasonic transducers which convert the electric energy supplied by a generator into ultrasonic frequency vibratory energy, which can then be applied to the tissue of a patient. Ultrasonic surgical instruments use relatively high-power, low-frequency vibratory energy, typically at a frequency range of about 20 kHz to about 100 kHz.
In general, ultrasonic soft tissue cutting and coagulation systems include a member that is coupled to the ultrasonic transducers, and that can be made to vibrate at ultrasonic frequencies. The ultrasonically vibrating probe is then applied to the tissue, in order to transmit ultrasonic energy to the tissue. In this way, the contacted tissue can be cut or coagulated. Ultrasonic surgical systems offer a number of advantages over conventional surgical systems, for example reduction of bleeding and trauma.
The mechanism through which the ultrasonic probe and the tissue interact, i.e. the physics of ultrasonic soft tissue cutting and coagulation, is not completely understood, however various explanations have been provided by researchers over the years. These explanations include descriptions of mechanical effects and thermal effects. The mechanical viewpoint states that the vibrating tip of the ultrasonic probe generates short-range forces and pressures, which are sufficient to dislodge cells in the tissue, and break up the tissue structures. Various types of forces are postulated as contributing to the rupture of the tissue layer, for example the impact forces resulting from the direct contact of the vibrating tip with tissue, and the shear forces that are the result of the differences in force levels across tissue boundaries. Some energy may be lost due to frictional heating, and by the heating caused by the absorption of acoustic energy by tissue.
Thermal effects may include frictional heat, generated by the ultrasonically vibrating tip, in an amount sufficient to melt a portion of the contacted tissue. Alternatively, the tissue may absorb the vibratory energy, which it then converts into heat. The generated heat may be used to coagulate a blood vessel, by way of example. Other effects that have been postulated in order to explain the probe-tissue interaction include cavitational effects. The cavitation viewpoint postulates that the coupling of ultrasonic energy onto tissue results in the occurrence of cavitation in tissue, namely the formation of gas or vapor-filled cavities or bubbles within the tissue, which may oscillate and propagate. A combination of mechanical, thermal, and cavitational effects may result in the desired surgical outcomes, such as cutting and coagulation.
A number of ultrasonic soft tissue cutting and coagulating systems have been disclosed in the prior art. For example, U.S. Pat. No. 5,322,055 (the “'055 patent”), assigned on its face to Ultracision, Inc., discloses ultrasonic surgical instruments having a non-vibrating clamp for pressing tissue against an ultrasonically vibrating blade, for cutting, coagulating, and blunt-dissecting of tissue. When ultrasonically activated, the blade undergoes longitudinal mode vibrations, parallel to the blade edge. U.S. Pat. No. 6,036,667 (the “'667 patent”), assigned on its face to United States Surgical Corporation and to Misonix Incorporated, discloses an ultrasonic dissection and coagulation system. The ultrasonic system includes an ultrasonic cutting blade, and a clamp member for clamping tissue in conjunction with the blade. The blade has a cutting surface that is angled with respect to the longitudinal axis of the elongated body portion of the system.
U.S. Pat. No. 6,056,735 (the “'735 patent”), assigned on its face to Olympus Optical Co., Ltd., relates to ultrasonic treatment systems, including endoscopic systems and aspiration systems, for treating living tissue. The '735 patent features an ultrasonic treatment system including a probe which conveys ultrasonic vibrations to a stationary distal member. The stationary distal member cooperate with a movable holding member to clamp or free tissue, when manipulated by a scissors-like manipulating means.
In the prior art patents discussed above, the ultrasonically vibrating member must cooperate with a clamp or jaw, in order to grasp the tissue that is being treated. It is desirable to provide systems having a blade/jaw assembly, in which the ultrasonically vibrating member can operate (in conjunction with the jaw) without having to perform, by itself, a grasping function.